Ron:
I was in a hurry to leave, just typed something pop-up in my head without checking myself. Anyway, I propose to answer aladdin76's question from strength point of view.
If the design was done by using the lower yield strength, then there is no apparent problem. However, if it is another way around, then the member loading capacity will be affected to some extent. The exact effect depends on the quantity of the lower yield bars vs the higher yield ones, and location and pattern of the mix. None of the above can be answered easily since the job is already done, at this juncture, I don't think it is overly conservative to re-compute the strength assuming all bars are to yield at the lowest strength level, thus, reduce the load carrying capacity significantly (almost 28% in this case, fy1/fy2 =380/297=1.279, M=f[Asfyd], assume constant As & d-difference small). Actually, for mixed grade application, after the lower yield strength is reached, the member would still have some additional load carrying capacity until the remaining steel has also yielded. But the total load capacity is still lower than the member reinforced completely with the higher grade bars. Please exam my logic, I think you would agree with me, at least to some extent.
For the case of new design - don't ever contemplate it (mixing two grades of steels).